Since Plato, most philosophers have drawn a sharp line
between reason and emotion, assuming that emotions interfere with
rationality and have nothing to contribute to good reasoning.
In his dialogue the Phaedrus, Plato compared the rational
part of the soul to a charioteer who must control his steeds,
which correspond to the emotional parts of the soul (Plato 1961,
p. 499). Today, scientists are often taken as the paragons of
rationality, and scientific thought is generally assumed to be
independent of emotional thinking.

But current research in cognitive science is increasingly challenging
the view that emotions and reason are antagonistic to each other.
Evidence is accumulating in cognitive psychology and neuroscience
that emotions and rational thinking are closely intertwined (see,
for example: Damasio 1994, Kahneman 1999, and Panksepp 1999).
My aim in this chapter is to extend that work and describe the
role of the emotions in scientific thinking. If even scientific
thinking is legitimately emotional, then the traditional division
between reason and emotion becomes totally unsupportable.

My chapter begins with a historical case study. In his famous
book, The Double Helix, James Watson presented a review
of the discovery of the structure of DNA. Unlike the typical dry
and scientific biography or autobiography, Watson provided a rich
view of the personalities involved in one of the most important
discoveries of the 20th century. I will present a survey and analysis
of the emotions mentioned by Watson and use it and quotations
from other scientists to explain the role of the emotions in scientific
cognition. My account will describe the essential contributions
of emotions in all three of the contexts in which scientific work
is done: investigation, discovery, and justification. Initially,
emotions such as curiosity, interest, and wonder play a crucial
role in the pursuit of scientific ideas. Moreover, when investigation
is successful and leads to discoveries, emotions such as excitement
and pleasure arise. Even in the third context, justification,
emotions are a crucial part of the process of recognizing a theory
as one that deserves to be accepted. Good theories are acknowledged
for their beauty and elegance, which are aesthetic values that
are accompanied by emotional reactions.

2 The Discovery of the Structure of DNA

In 1951, James Watson was a young American postdoctoral fellow
at Cambridge University. He met Francis Crick, a British graduate
student who was already in his mid- 30s. Both had a strong interest
in genetics, and they began to work together to identify the structure
of the DNA molecule and to determine its role in the operations
of genes. The intellectual history of their work has been thoroughly
presented by Olby (1974) and Judson (1979). My concern is with
emotional aspects of the thinking of Watson and Crick and of scientific
thinking in general; these aspects have been largely ignored by
historians, philosophers, and even psychologists. The primary
question is: What role did emotions play in the thinking of Watson
and Crick that led to the discovery of the structure of DNA and
the acceptance of their model?

In order to answer this question, I read carefully through The
Double Helix, looking for words that refer to emotions. Watson
described not only the ideas and the hypotheses that were involved
in the discovery of the structure of DNA, but also the emotions
that accompanied the development of the new ideas. In Watson's
(1969) short book, whose paperback edition has only 143 pages,
I counted a total of 235 emotion words. Of the 235 emotion episodes
referred to, more than half (125) were attributed by Watson solely
to himself. Another 35 were attributed to his collaborator Francis
Crick, and 13 emotions were attributed by Watson to both of them.
There were also 60 attributions of emotions to other researchers,
including various scientists in Cambridge and London. I coded
the emotions as having either positive valence (e.g. happiness)
or negative valence (e.g. sadness), and found that more than half
of the emotions (135) had positive valence. Of course, there is
no guarantee that Watson's reports of the emotions of himself
and others are historically and psychologically accurate, but
they provide a rich set of examples of possible emotional concomitants
of scientific thinking.

In order to identify the kinds of emotions mentioned by Watson,
I coded the emotion words in terms of what psychologists call
basic emotions, which are ones taken to be culturally universal
among human beings (Ekman 1992). The usual list of basic emotions
includes happiness, sadness, anger, fear, disgust, and sometimes
surprise. To cover classes of emotion words that occurred frequently
in the book but did not fall under the 6 basic emotions, I added
3 additional categories: interest, hope, and beauty. Figure 1
displays the frequency with which these categories of emotions
appear in Watson's narrative. Happiness was the most frequently
mentioned emotion, occurring 65 times with many different words
referring to such positive emotional states as excitement, pleasure,
joy, fun, delight, and relief. The next most frequently mentioned
classes of emotions were: interest, with 43 emotion words referring
to states such as wonder and enthusiasm; and fear, with 38 emotion
words referring to states such as worry and anxiety.

The point of this study, however, was not simply to enumerate
the emotion words used by Watson in his story. To identify the
role that emotions played in the thinking of Watson and Crick,
I coded the emotion words as occurring in three different contexts
of the process of inquiry: investigation , discovery, and justification.
Most scientific work occurs in the context of investigation, when
scientists are engaged in the long and often difficult attempt
to establish empirical facts and to develop theories that explain
them. Much preparatory experimental and theoretical work is usually
required before scientists are able to move into the context of
discovery, in which new theoretical ideas and important new empirical
results are produced. Finally, scientists enter the context of
justification, when new hypotheses and empirical results are evaluated
with respect to alternative explanations and the entire body of
scientific ideas.

Figure 1. Frequency of classes of emotion words in Watson
(1969).

The distinction between the contexts of discovery and justification
is due to Reichenbach (1938). I use it here not to demarcate the
psychological and subjective from the philosophical and rational,
as Reichenbach intended, but merely to mark different stages in
the process of inquiry, all of which I think are of both psychological
and philosophical interest. I further divide Reichenbach's context
of discovery into contexts of investigation and discovery, in
order to indicate that much work is often required before actual
discoveries are made. In scientific practice, the contexts of
investigation, discovery, and justification often blend into each
other, so they are best viewed as rough stages of scientific inquiry
rather than as absolutely distinct.

Most of Watson's emotion words (163) occurred in the context of
investigation. 15 words occurred in the context of discovery,
29 in the context of justification, and 28 emotion words occurred
in other more personal contexts that had nothing to do with the
development of scientific ideas. In the rest of this chapter,
I will provide a much more detailed account of how the many different
kinds of emotions contribute to scientific thinking in the three
contexts. I will offer not only a correlational account of what
emotions tend to occur in what contexts, but also a causal account
of how emotions produce and are produced by the cognitive operations
that occur in the different stages of scientific inquiry.

3 Emotions in the Context of Investigation

Discussions of scientific rationality usually address questions
in the context of justification, such as when is it rational to
replace a theory by a competing one. But scientists engage in
a great deal of decision making that precedes questions of justification.
Students who are interested in pursuing a scientific career must
make decisions that answer questions such as the following: What
science (e.g. physics or biology) should I concentrate on? What
area of the science (e.g. high-energy physics or molecular biology)
should I focus on? What particular research topics should I pursue?
Which questions should I attempt to answer? What methods and tools
should I use in attempting to answer those questions?

On the traditional view of rational decision making familiar from
economics, scientists should attempt to answer these questions
by calculating how to maximize their expected utility. This involves
taking into account scientific goals such as truth and understanding,
and possibly also taking into account personal goals such as fame
and financial gain, as well as considering the probabilities that
particular courses of research will lead to the satisfaction of
these goals. Some philosophers (e.g. Goldman 1999 and Kitcher
1993) describe scientists as choosing projects based on maximizing
epistemic goals such as truth.

I would like to propose an alternative view of scientific decision
making in the context of investigation. Decisions concerning what
topics to research are much more frequently based on emotions
than on rational calculations. It is rarely possible for scientists
to predict with any accuracy what choice of research areas, topics,
and questions will pay off with respect to understanding, truth,
or personal success. The range of possible actions is usually
ill-specified, and the probabilities of success of different strategies
are rarely known. Because rational calculation of maximal utility
is effectively impossible, it is appropriate that scientists rely
on cognitive emotions such as interest and curiosity to shape
the direction of their inquiries. See Thagard (forthcoming) for
a model of decision making as informed intuition based on emotional
coherence.

Watson's narrative makes it clear that he and Crick were heavily
motivated by interest. Watson left Copenhagen where his postdoctoral
fellowship was supposed to be held because he found the research
being done there boring: the biochemist he was working with there
"did not stimulate me in the slightest" (Watson 1969,
p. 23). In contrast, he reacted to questions concerning the physical
structure of biologically important molecules such as DNA with
emotions such as excitement: "It was Wilkins who first excited
me about X-ray work on DNA" (p. 22); "Suddenly I was
excited about chemistry" (p. 28). Crick similarly remarks
how he and Watson "passionately wanted to know the details
of the structure" (Crick 1988, p. 70).

Once interest and curiosity direct scientists to pursue answers
to particular questions, other emotions such as happiness and
hope can help motivate them to perform the often laborious investigations
that are required to produce results. It was clearly important
to Watson and Crick that they often became excited that they were
on the right track. Watson (1969, p. 99) wrote that "On a
few walks our enthusiasm would build up to the point that we fiddled
with the models when we got back to our office." Both took
delight in getting glimpses of what the structure of DNA might
be. They were strongly motivated by the hope that they might make
a major discovery. Hope is more than a belief that an event might
happen ­ it also the emotional desire and joyful anticipation
that it will happen. I counted 26 occurrences where Watson mentioned
the hopes of himself or others for scientific advance.

In addition to positive emotions such as interest and happiness,
scientists are also influenced by negative emotions such as sadness,
fear, and anger. Sadness enters the context of investigation when
research projects do not work out as expected. Watson and Crick
experienced emotions such as dismay when their work faltered.
Such emotions need not be entirely negative in their effects,
however, because sadness about the failure of one course of action
can motivate a scientist to pursue an alternative and ultimately
more successful line of research.

Fear can also be a motivating emotion. Watson and Crick were very
worried that the eminent chemist Linus Pauling would discover
the structure of DNA before they did, and they also feared that
the London researchers, Rosalind Franklin and Maurice Wilkins,
would beat them. Watson wrote that when he heard that Pauling
had proposed a structure, "my stomach sank in apprehension
at learning that all was lost" (p. 102). Other worries and
anxieties arose from setbacks experienced by Watson and Crick
themselves. Watson was initially very excited by a proposal that
was shown by a crystallographer to be unworkable, but tried to
salvage his hypothesis: "Thoroughly worried, I went back
to my desk hoping to salvage the like-with-like idea" (p.
122).

The other negative emotion that Watson mentions frequently in
the context of investigation is anger. To himself, Watson ascribes
only weak forms of anger, such as annoyance and frustration, but
he describes Crick as experiencing fury and outrage when his senior
professors wrote a paper that failed to acknowledge his contributions.
According to Oatley (1992), people experience anger when accomplishment
of their goals is blocked by people or events. Most of the anger-related
episodes mentioned by Watson are directed at people, but some
concern facts, as when Watson and Crick both become annoyed at
the complexity of DNA bonds. I do not get the impression from
Watson's chronicle that anger was ever a motivating force in the
scientific work he described, but we can see it as an effect of
undesirable interactions with other people and the world.

A general model of the role of emotions in the context of investigation
of scientific investigations is shown in figure 2. Interest, wonder,
curiosity and the avoidance of boredom are key inputs to the process
of selecting of scientific questions to investigate. I have made
the causal arrows between emotions and the process of question
generation bidirectional in order to indicate that emotions are
outputs as well as inputs to the generation of questions. Coming
up with a good question can increase curiosity and interest, and
produce happiness as well. Once questions have been generated,
the cognitive processes involved in trying to generate answers
to them can also interact with emotions such as interest and happiness,
as well as with negative emotions such as fear. For convenience,
I have organized positive emotions on the left side of figure
2, and negative emotions on the right side. The causal arrows
connecting processes of question generation, question answering,
and answer evaluation are also bidirectional, indicating interconnections
rather than a linear operation. For example, the attempt to answer
a question can generate subordinate questions whose answers are
relevant to the original question. For a discussion of the process
of question generation in science, see Thagard (1999).

The emotions that Watson attributed to himself and his colleagues
are commonly found in other scientists, as evident in a serious
of interviews conducted by the biologist Lewis Wolpert for BBC
Radio (Wolpert and Richards 1997). Wolpert elicited frank descriptions
of leading researchers' intense emotional involvement in their
work. For example, the distinguished biologist Gerald Edelman
stated: "Curiosity drives me. I believe that there is a group
of scientists who are kind of voyeurs, they have the splendid
feeling, almost a lustful feeling, of excitement when a secret
of nature is revealed ... and I would certainly place myself in
that group." (Wolpert and Richards 1997, p. 137) Similarly,
the eminent physicist Carlo Rubbia said of scientists: "We're
driven by an impulse which is one of curiosity, which is one of
the basic instincts that a man has. So we are essentially driven
not by how can I say not by the success, but by a sort of passion,
namely the desire of understanding better, to possess, if you
like, a bigger part of the truth" (Wolpert and Richards,
1997, p. 197).

Figure 2. A model of the causal interconnections of
cognitive processes of inquiry and emotional states. Arrows indicate
causal influences.

According to Kubovy (1999, p. 147), to be curious is to get
pleasure from learning something that you did not previously know.
He contends that curiosity has its roots in animal behavior, having
evolved from the need to search for food. Many mammals prefer
richer environments over less complex ones. Humans can be curious
about a very wide range of subjects, from the trivial to the sublime,
and scientists direct their intense drive to learn things that
are unknown not just to them, but to people in general. Loewenstein
(1994) defends a more cognitive account of curiosity as the noticing
of knowledge gaps, but underplays the emotional side of curiosity.
There are many knowledge gaps that scientists may notice, but
only some of them arouse an emotional interest that spurs them
to the efforts required to generate answers.

4 Emotions in the Context of Discovery

The discovery of the structure of DNA occurred after Maurice
Wilkins showed Watson new X-ray pictures that Rosalind Franklin
had taken of a three-dimensional form of DNA. Watson reports:
"The instant I saw the picture my mouth fell open and my
pulse began to race" (p. 107). This picture moved Watson
from the context of investigation into the context of discovery,
in which a plausible hypothesis concerning the structure of DNA
could be generated. While drawing, Watson got the idea that each
DNA molecule might consist of two chains, and he became very excited
about the possibility and its biological implications. Here is
a passage that describes his resulting mental state; I have highlighted
in boldface the positive emotion words and in italics the negative
emotion words.

As the clock went past midnight I was becoming more and more pleased.
There had been far too many days when Francis and I worried
that DNA structure might turn out to be superficially very dull,
suggesting nothing about either its replication or its function
in controlling cell biochemistry. But now, to my delight
and amazement, the answer was turning out to be profoundly
interesting. For over two hours I happily lay awake
with pairs of adenine residues whirling in front of my closed
eyes. Only for brief moments did the fear shoot through
me that an idea this good could be wrong. (Watson 1969, p. 118)

Watson's initial idea about the chemical structure of DNA turned
out to be wrong, but it put him on the track that quickly led
to the final model that Watson and Crick published.
Most of the emotions mentioned by Watson in his discussion of
discoveries fall under the basic emotion of happiness; these include
excitement, pleasure and delight. The chemist who helped to invent
the birth control pill, Carl Djerassi, compares making discoveries
to sexual pleasure. "I'm absolutely convinced that the pleasure
of a real scientific insight - it doesn't have to be a great discovery
- is like an orgasm" (Wolpert and Richards 1997, p. 12).
Gopnik (1998) also compares explanations to orgasms, hypothesizing
that explanation is to cognition as orgasm is to reproduction.

The pleasure of making discoveries is effusively described by
Gerard Edelman:
After all, if you been filling in the tedium of everyday existence
by blundering around a lab, for a long time, and wondering how
you're going to get the answer, and then something really glorious
happens that you couldn't possibly have thought of, that has to
be some kind of remarkable pleasure. In the sense that it's a
surprise, but it's not too threatening, it is a pleasure in the
same sense that you can make a baby laugh when you bring an object
of nowhere Breaking through, getting various insights is certainly
one of the most beautiful aspects of scientific life. (Wolpert
and Richards 1997, p. 137)

Carlo Rubbia reports that "The act of discovery, the act
of being confronted with a new phenomenon, is a very passionate
and very exciting moment in everyone's life. It's the reward for
many, many years of effort and, also, of failures" (Wolpert
and Richards 1997, p. 197).
François Jacob (1988, p. 196-197) describes his first taste
of the joy of discovery as follows: "I had seen myself launched
into research. Into discovery. And, above all, I had grasped the
process. I had tasted the pleasure." Later, when Jacob was
developing the ideas about the genetic regulatory mechanisms in
the synthesis of proteins that later won him a Nobel Prize, had
an even more intense emotional reaction: "These hypotheses,
still rough, still vaguely outlined, poorly formulated, stir within
me. Barely have I emerged that I feel invaded by an intense joy,
a savage pleasure. A sense of strength, as well, of power"
(Jacob 1988, p. 298). Still later, Jacob describes the great joy
that came with experimental confirmation of his hypotheses. Scheffler
(1991, p. 10) discusses the joy of verification, when scientists
take pleasure when their predictions are found to be true. Of
course, predictions sometimes turn out to be false, producing
disappointment and even gloom.

It is evident from Watson and the other scientists that I have
quoted that discovery can be an intensely pleasurable experience.
In figure 2, I have shown surprise and happiness as both arising
from the successful generation of answers to pursued questions.
The prospect of being able to experience such emotions is one
of the prime motivating factors behind scientific efforts. Richard
Feynman proclaimed that his work was not motivated by a desire
for frame or prizes such as the Nobel that he eventually received,
but by the joy of discovery: "The prize is the pleasure of
finding a thing out, the kick of the discovery, the observation
that other people use it [my work]-those are the real things,
the others are unreal to me (Feynman 1999, p. 12). Discoveries
are usually pleasant surprises, but unpleasant surprises also
occur, for example when experiments yield data that are contrary
to expectations. Disappointment and sadness can also arise when
the evaluation stage leads to the conclusion that one's preferred
answers are inferior or inadequate, as shown in figure 2.

Kubovy (1999) discusses virtuosity, the pleasure we have when
we are doing something well. He thinks that humans and also animals
such as monkeys and dolphins enjoy working and take pleasure in
mastering new skills. Scientists can achieve virtuosity in many
diverse tasks such as designing experiments, interpreting their
results, and developing plausible theories to explain the experimental
results. According to physicist Murray Gell-mann, "Understanding
things, seeing connections, finding explanations, discovering
beautiful, simple principles that work is very, very satisfying"
(Wolpert and Richards 1997, p. 165).

5 Emotions in the Context of Justification

Although many would concede that the processes of investigation
and discovery are substantially emotional, it is much more radical
to suggest that even the context of justification has a strong
emotional component. In Watson's writings, the main sign of an
emotional component to justification is found in his frequent
description of the elegance and beauty of the model of DNA that
he and Crick produced. Watson wrote:

We only wished to establish that at least one specific two-chain
complementary helix was steroeochemically possible. Until this
was clear, the objection could be raised that, although our idea
was aesthetically elegant, the shape of the sugar-phosphate backbone
might not permit its existence. Happily, now we knew that this
was not true, and so we had lunch, telling each other that a structure
this pretty just had to exist. (p. 131)

Thus one of the causes of the conviction that they had the right
structure was its aesthetic, emotional appeal. Other scientists
also had a strong emotional reaction to the new model of DNA.
Jacob (1988, p. 271) wrote of the Watson and Crick model: "This
structure was of such simplicity, such perfection, such harmony,
such beauty even, and biological advances flowed from it with
such rigor and clarity, that one could not believe it untrue."
In a similar vein, the distinguished microbiologist Leroy Hood
described how he takes pleasure in coming up with elegant theories:

Well, I think it's a part of my natural enthusiasm for everything,
but what I've been impressed with in science over my twenty-one
years is the absolute conflict between, on the one hand, as we
come to learn more and more about particular biological systems
there is a simple elegant beauty to the underlying principles,
yet when you look into the details it's complex, it's bewildering,
it's kind of overwhelming, and I think of beauty in the sense
of being able to extract the fundamental elegant principles from
the bewildering array of confusing details, and I've felt I was
good at doing that, I enjoy doing that. (Wolpert and Richards
1997, p. 44).

Many other scientists have identified beauty and elegance as distinguishing
marks of theories that should be accepted (McAllister 1996).

From the perspective of traditional philosophy of science, or
even the perspective of traditional cognitive psychology that
separates the cognitive and the emotional, the fact that scientists
find some theories emotionally appealing is irrelevant to their
justification. My own previous work is no exception: I have defended
the view that scientific theories are accepted or rejected on
the basis of their explanatory coherence with empirical data and
other theories (Thagard 1992, 1999). But my new theory of emotional
coherence shows how cognitive coherence judgments can generate
emotional judgments (Thagard 2000, ch. 6). I will now briefly
review the theory of emotional coherence and indicate how it can
be applied to explain emotional scientific judgments concerning
the acceptance of theories.

My coherence theory of inference can be summarized in the following
theses (Thagard and Shelley forthcoming; see also Thagard 2000):

1. All inference is coherence-based. So-called rules of inference
such as modus ponens do not by themselves license inferences,
because their conclusions may contradict other accepted information.
The only rule of inference is: Accept a conclusion if its acceptance
maximizes coherence.
2. Coherence is a matter of constraint satisfaction, and can be
computed by connectionist and other algorithms.
3. There are six kinds of coherence: analogical, conceptual, explanatory,
deductive, perceptual, and deliberative.
4. Coherence is not just a matter of accepting or rejecting a
conclusion, but can also involve attaching a positive or negative
emotional assessment to a proposition, object, concept, or other
representation.

On this account, a theory is justified if inferring it maximizes
coherence, but assessment can also involve an emotional judgment
Theories consists of hypotheses which are comprised of concepts.
According to the theory of emotional coherence, these representations
not only have a cognitive status of being accepted or rejected,
they also have an emotional status of being liked or disliked.
In keeping with Bower's (1981) account of the psychology of emotions,
I call its emotional status the valence of the representation.
A representation receives its valence as the result of its connections
with other representations. The valence of a theory will flow
from the valences of the hypotheses that constitute it, as well
as from the overall coherence that it generates.
Overall coherence requires a judgment about how everything fits
together. Such judgments can be made by the computational model
HOTCO ("hot coherence"), which not only simulates the
spread of valences among representations, but also simulates how
the coherence of the representations with each other can generate
a "metacoherence" inference which is associated with
happiness. I will not repeat the computational details (Thagard
2000), but merely want here to give the general flavor of how
the model works. A proposition is highly coherent with other propositions
if its acceptance helps to maximize the satisfaction of constraints,
such as the constraint that if a hypothesis explains a piece of
evidence, then the hypothesis and the evidence should be either
accepted together or rejected together. If a group of propositions
can be accepted together in such a way that the individual propositions
each tend to satisfy a high proportion of the constraints on them,
the overall system of proposition gets a high metacoherence rating
Figure 3 diagrams how judgments of coherence and other emotions
can arise. Units are artificial neurons that represent propositions,
and their assessment by neural network algorithms for maximizing
constraint satisfaction leads to them either being accepted or
rejected. In addition, the extent to which the constraints on
a unit are satisfied affects how much it activates a unit representing
a judgment of coherence, which produces happiness. For example,
if the acceptance of a hypothesis makes possible satisfaction
of numerous constraints that tie the hypotheses with the evidence
it explains, then a unit representing the hypothesis will strongly
activate the coherence node and the thence the happiness node.
At the other end of the emotional distribution, incoherence tends
to produce unhappiness or even fear-related emotions such as anxiety.

This sketch of the theory and computational model of emotional
coherence shows how it is possible for a mind simultaneously to
make cognitive judgments and emotional reactions. Watson and Crick's
hypothesis concerning the structure of DNA was highly coherent
with the available evidence and with the goals of biologists to
understand the genetic basis of life. This high coherence generated
not only a judgment that the hypothesis should be accepted, but
also an aesthetic, emotional attitude that the hypothesis was
beautiful. Coherence made Watson, Crick, Jacob and others very
happy.

6 Conceptual Change as Emotional Change

Discovering the structure of DNA was a major scientific breakthrough,
but it was not a major case of conceptual change. The discovery
brought about additions to the concepts of a gene and DNA, but
did not require revisions of previous components of the concepts.
New hypotheses were adopted, but there was no rejection of previously
believed hypotheses. In contrast, scientific revolutions involve
both major alteration of concepts and revision of previously held
hypotheses (Thagard 1992). I will now argue that conceptual changes
also often involve emotional change.
Consider, for example, Darwin's theory of evolution by natural
selection. When he proposed it in the Origin of Species
in 1859, some scientists such as Huxley quickly realized the strength
of the theory and adopted it. But others continued to maintain
the traditional view that species arose by Divine creation, and
viewed Darwin's theory as not only false but repugnant. Even today,
there are creationists who view the theory of evolution as not
only false but evil, since they see it as undermining religious
beliefs and values. Most biologists, in contrast, feel that Darwin's
theory is profound and elegant. Thus for a creationist to become
a Darwinian, or for a Darwinian to become a creationist, thinkers
must undergo emotional as well as cognitive changes. In addition
to rejecting some hypotheses already held and accepting new ones,
thinkers who are changing theories are also changing their emotional
attitudes towards propositions, concepts, and even people: there
are different emotions associated with Darwin-as-scientific-hero
and Darwin-as-heretic.

Consider also the more recent historical case of the initial rejection
and eventual acceptance of the bacterial theory of ulcers (Thagard
1999). When Marshall and Warren (1984) proposed that most peptic
ulcers are caused by the newly discovered bacterium now known
as Helicobacter pylori, their hypothesis was initially
viewed as not only implausible, but even crazy! Marshall's persistent
advocacy of the unpopular hypothesis led people to view him as
brash and irresponsible. But annoyance turned to respect as evidence
mounted that eradicating the bacteria brought many people a permanent
cure of their ulcers. Not only did attitudes change toward Marshall
but also towards the bacterial theory of ulcer and towards the
concept of ulcer-causing bacteria. What was ridiculed became appreciated
as an important part of medical theory and practice.

I propose that these changes come about through the process of
achieving emotional coherence. At the same time that decisions
concerning what to believe are made by a process that maximizes
explanatory coherence (fitting hypotheses with data and each other),
attitudes are formed by a process that spreads valences through
the representational system in accord with existing valences and
emotional constraints. For example, scientists who come to appreciate
the explanatory power of Darwin's evolutionary hypotheses will
come to believe them and to attach a positive emotional valence
to them, to the concept of evolution, and to Darwin. On the other
hand, scientists (if there are any) who adopt religious fundamentalism
and decide that the Bible is to be revered will reject the hypothesis
and concept of evolution and view it as odious. Our beliefs are
revised by a holistic process of deciding what fits with what,
and our emotions are similarly adjusted.

If conceptual change in science is often emotional change, what
about science education? Often, science education will not require
emotional change because students do not have any emotional attachments
to prescientific ideas. For example, learning to use Newton's
laws of motion to understand the behavior of projectiles does
not seem to require abandoning any emotional attachment on the
part of the students to Aristotelian ideas. But learning in biology
and the social sciences may involve much more emotional adjustment.
Biology students learning about genetics and evolution may have
to abandon beliefs that they not only hold but value about the
nature of the universe. Similarly, social and political beliefs
may be factual, but they are closely intertwined with strongly
emotional values. A microeconomist who is convinced that laissez-faire
capitalism is the best economic system differs in beliefs and
also emphatically in values from a macroenomist who favors socialism.
Hence educators should be alert for cases where resistance to
conceptual change derives from emotional as well as cognitive
factors. Normally, emotional change is more the province of psychotherapists
than science teachers, but teaching emotionally laden scientific
issues such as the theory of evolution may require therapeutic
techniques to identify valences as well as beliefs. Appreciation
of radically different conceptual frameworks, for example traditional
Chinese medicine from the perspective of western medicine, may
require emotional as well as conceptual flexibility (Thagard and
Zhu, forthcoming).

7 Should Scientists be Emotional?

But should it not be the job of science educators to help
students aspire to what scientists are supposed to be: objective
and nonemotional reasoners? Even if emotions are associated with
scientific thinking, perhaps the aim of scientific education,
from grade school through the Ph.D., should be to inculcate in
students the necessity of eradicating subjective emotions in order
to improve their scientific thinking by insulating it from bias.
It is not hard to find cases where emotions have distorted science,
such as Nazis rejecting Einstein's theory of relativity because
they hated Jews, and researchers fabricating data because they
wanted to be famous.

While recognizing that there are many such cases in which emotions
have undermined scientific objectivity and truth-seeking, I think
it would be a mistake to demand that scientists strive to eliminate
emotions from the cognitive processes enable them to do science.
First, severing the cognitive from the emotional is probably impossible.
As I mentioned in the introduction, there is abundant evidence
from psychology and neuroscience that cognitive and emotional
processes are intimately intertwined. The ethical principle that
ought implies can applies: we cannot insist that a person's
thinking should be emotion-free when it is biologically impossible
for people to think that way. Mitroff (1974, p. 99) found in his
study of Apollo moon scientists that they held strongly emotional
views, especially of other researchers, but concluded that "the
existence of such strong emotions does not prevent scientists
from doing excellent scientific work."

Second, even if scientists could become free of the sway of emotions,
it is likely that science would suffer as a result. The discussion
above of emotions in the contexts of investigation and discovery
showed that positive emotions such as happiness and even negative
emotions such as anxiety play an important role in motivating,
energizing and directing science. Given that science is often
difficult and frustrating, why would anyone do it if it were not
also sometimes exciting and satisfying? According to Mitroff (1974,
p. 248): "To eliminate strong emotions and intense commitments
may be to eliminate some of science's most vital sustaining forces."
Even in the context of justification, there is a useful cognitive
contribution of feelings of elegance and beauty, because they
are attached to theories that excel in explanatory coherence,
which, I would argue, is what scientific theory is intended most
immediately to maximize. An interesting open question is how the
training of scientists might be expanded to include enhancement
of the kinds of emotional responses that foster good scientific
research. I suspect that most such training occurs implicitly
during the interactions between budding researchers and their
mentors, through a kind of contagion of taste and enthusiasm.
It is possible, however, that scientists individually possess
sets of inherited and learned emotional dispositions that are
impervious to emotional training.

In conclusion, I would emphatically not urge that scientists aim
to become robotically unemotional. Despite dramatic increases
in computer speed and intelligent algorithms, computers currently
are no threat to replace scientists. A key aspect of intelligence
that is rarely recognized is the ability to set new goals, not
just as ways of accomplishing other existing goals, but as novel
ends in themselves. There is no inkling in the field of artificial
intelligence of how computers could acquire the ability to set
goals for themselves, which is probably just as well because there
is no guarantee that the goals of such artificially ultra-intelligent
computers would coincide with the goals of human beings. In humans,
the development of non-instrumental goals is intimately tied with
emotions such as interest, wonder, and curiosity, which are just
the goals that spur scientists on. As the eminent neurologist
Santiago Ramón y Cajal (1999, p. 7) asserted: "All
outstanding work, in art as well as in science, results from immense
zeal applied to a great idea." A scientist without passion
would be at best a mediocre scientist.

Acknowledgments: I am grateful to Peter Carruthers and
Cameron Shelley for comments, and to the Natural Sciences and
Engineering Research Council of Canada for financial support.